The present application describes systems and techniques relating to storing data in non-volatile memory devices, for example, program pulsing in flash memory.
Non-volatile memory devices include random access memory (RAM) devices and read-only memory (ROM) devices. Traditionally, a ROM device was not generally re-writable. For example, an early type of programmable ROM used one time programmable (OTP) memory cells having a diode or a transistor with a fuse or an antifuse to store a bit of data.
Traditional electrically programmable read-only memory (EPROM) included one time programmable cells that used trapped charges underneath transistor gates to store data by changing transistor threshold voltage. EPROM cells were made erasable through the use of ultraviolet (UV) light to reduce or remove trapped charges. This UV erasing made EPROM cells re-writable.
Later developments included the electrically erasable programmable read-only memory (EEPROM) and flash memory, which may be programmed while in circuit on a printed circuit board. The EEPROM cell and the flash cell each include a transistor that uses a floating gate to store a charge. This charge may be applied (programmed) or removed (erased) as desired. Thus, many non-volatile memories are fully re-writable, despite being labeled as ROMs.
In addition, some non-volatile memories are multi-level memories capable of storing more than one bit of data in each storage cell. For example, multi-level cell (MLC) flash memories have been developed by Intel Corporation, located at 2080 Mission College Boulevard, Santa Clara Calif., 95052-8119. These flash memories store two bits of data in each cell using four memory states instead of the traditional two memory states in single-bit cell (SBC) memories.
In many non-volatile memories, a charge pump in the same circuit is used to generate voltage and current to program or erase storage cells in the memory. Typically, these storage cells are programmed in parallel in groups of cells. For a given voltage level, a programming time period is needed to program the storage cells in a group.